The long-term objectives of this program are to identify and to characterize the psychologic, pharmacologic, and evironmental variables which affect drug dependence. The immediate goals are: 1) to define the behavioral factors which influence the initiation and perpetuation of self administration of drugs in the rhesus monkey, 2) to characterize for drugs of dependence those pharmacologic properties which influence (i.e., increase or decrease) their ability to reinforce self- administration behavior, 3) to determine the behavioral and physiological consequences of acute and chronic intoxication with drugs of dependence, 4) to investigate the mechanism of tolerance and physical dependence and to evaluate the role of these factors in continuing self-administration of various drugs of dependence, and, 5) to study the interactions of various drugs of dependence with themselves and with other classes of drugs. Although a variety of drugs will be studied eventually, the initial studies will focus on the prototype drugs of each of the following pharmacologic classes: narcotic analgesics and antagonists (i.e., morphine, codeine, pentazocine, nalorphine, naloxone), depressants (i.e., barbiturates, ethanol), and stimulants (i.e., cocaine, amphetamines).